As the use of digital communications has increased over the past few decades, engineers have been faced with the challenge of building receivers and transmitters that are of a practical size and reasonable cost. While driven in the past to reduce size and cost, a large portion of the marketplace was composed of users--such as the military--that required small to moderate quantities of a particular receiver model. In addition, requirements for substantial capability/functionality and extreme environmental/reliability characteristics resulted in receivers that were large and bulky: albeit they were virtually "bullet-proof". The marketplace has now changed and a large part of the user community is composed of the commercial sector. As such, the requirements placed on communication equipment have also changed with increased pressure to meet price points acceptable for high volume product markets. Within this market, simpler receivers and transmitters with very focused functionality, low power consumption, and reduced size are desired, and the object of the invention is to provide receivers meeting this criteria.
The receiver disclosed herein is called the Integrated Receiver (IR.) The name reflects both its inherent nature for overlapping several receiver processes within a common processing path and its amenability for implementation using highly integrated circuitry. The IR's operating advantages stem from its unique signal processing characteristics that are achieved through novel use of charge coupled devices (CCD) technology and integrated tracking loop techniques.
The transmitter disclosed herein also has unique signal processing characteristics that are achieved through novel use of CCD technology.
CCD technology has been used for many years. Probably, its most notable application has been in the camera industry. However, recent advances in CCD design and fabrication have led designers to consider new uses for this technology. For example, see Weinberg et al. U.S. Pat. No. 5,126,682, which relates to a demodulation system incorporating CCD devices, which is incorporated herein by reference.
The CCD is a combination of analog and digital circuitry whose properties exploit the best from both worlds. Its analog input matches well with wideband and narrow-filtered signals provided by receiver front-ends and the device is capable of directly producing a digital output when integrated with an A/D converter. Furthermore, the device may be controlled and clocked digitally thereby providing a natural interface with a system processor. When configured as a transversal filter (see U.S. Pat. No. 5,126,682), the CCD offers several key features including:
Wideband input. PA1 Wide input dynamic range. PA1 Variable, low-to-high clocking speeds, KHz-to-.gtoreq.100 MHz. PA1 Variable/fixed tap weights. PA1 Multibit tap weights. PA1 Large number of stages. PA1 Programmable length control. PA1 Auxiliary, unique change domain processing functions. PA1 Filter, PA1 Frequency translate and modulate or demodulate, PA1 Equalize PA1 Store samples, PA1 Decimate, PA1 Despread, PA1 Tune, PA1 Amplify/Attenuate,
Given the features noted above, the CCD becomes an extremely useful device for receivers and transmitters as disclosed herein. Through its proper use, the device can:
incoming signals. The IR exploits the CCD's features so as to simplify digital signal processing requirements within the receiver.
When used in a transmitter, the CCD can filter, modulate, tune, spread and amplify/attenuate the signal for the purpose of generating a waveform for supplying to a power amplifier and antenna for transmission. This invention simplifies the modulation/tuning process.